The 39-year-old “semi-retired” trader has been living in the Archives, at 666 Greenwich (Monica Lewinsky’s former digs), since 1997. He loves the building and said he had no problems with any of the tenants until Ms. Armstrong’s arrival in March 2004. In fact, it wasn’t until a night in March 2006 that Mr. Rehder realized that he was disturbing anyone.

“I came back to my place with some friends late at night and started playing music,” he told The Observer. “All of a sudden, there was an intense banging on the door. I realized that the music was loud and went to the door kind of with my tail between my legs. As soon as I opened it, this person started screaming at me. I tried to apologize, but she wouldn’t listen.”

Ms. Armstrong has a different account of that night.

Court documents state that she called the front desk at about 1 a.m. to complain about Mr. Rehder’s music. No one was available to come up, so a guest of Ms. Armstrong’s went next-door to complain. Mr. Rehder became threatening, so the guest returned to the apartment. A few minutes later, Ms. Armstrong heard Mr. Rehder’s doorbell being rung repeatedly.

Thinking that it was someone from the front desk, according to court documents, she opened the door—and found Mr. Rehder ringing his own doorbell in an effort to drive Ms. Armstrong from her apartment.

“She’s insane,” Mr. Rehder told The Observer. “That stuff about me being threatening and ringing my own doorbell is an absolute, insane lie.”

Court documents show that from September 2005 to August 2006, Ms. Armstrong formally complained about the loud music coming from her neighbor’s apartment at least 17 times.

Mr. Rehder said that he received three or four complaints, including one after the March incident, and remedied every problem. “They told me that I couldn’t play music later than 11 p.m., and from then going forward, I never played music later than that.”

Ms. Armstrong has since moved out of the Archives. Her attorney, Eric Sherman, relayed to The Observer that she is “delighted with the judgment.”

“I find this all just bizarre, and I feel sorry for Rockrose,” Mr. Rehder said of the Archives’ landlord, Rockrose Development. “If they appeal, I will go to court to testify.”